Development and application of helium-filled soap bubbles: For large-scale PIV experiments in aerodynamics

A new type of tracer is making its entry in the scenario of wind-tunnel measurements: helium-filled soap bubbles (HFSB). The present work discusses the main fluid-dynamic and optical properties of HFSB to evaluate their use for quantitative measurements in aerodynamic experiments.<br/>In the past three decades, particle image velocimetry (PIV)...

Helium-filled soap bubbles for vortex core velocimetry

Velocity measurements within the core of high-swirl vortices are often hampered by heavier-than-air particle tracers being centrifuged outside the vortex core region. The use of neutrally buoyant and lighter-than-air tracers is investigated to aim at homogeneous tracers concentration in air flow experiments dealing with high-swirl vortices...

HFSB-seeding for large-scale tomographic PIV in wind tunnels

A new system for large-scale tomographic particle image velocimetry in low-speed wind tunnels is presented. The system relies upon the use of sub-millimetre helium-filled soap bubbles as flow tracers, which scatter light with intensity several orders of magnitude higher than micron-sized droplets. With respect to a single bubble generator,...

Statistical Characterization of Helium-Filled Soap Bubbles Tracing Fidelity for PIV

The present work follows a previous study on the aerodynamic characterization of helium-filled soap bubbles (HFSBs) for large-scale PIV measurements. HFSBs were found to yield, on average, a time response of about 10s. However, the response of each individual tracer remained to be ascertained, which is the topic of the present study. The...

Large-scale volumetric pressure from tomographic PTV with HFSB tracers

The instantaneous volumetric pressure in the near-wake of a truncated cylinder is measured by use of tomographic particle tracking velocimetry (PTV) using helium-filled soap bubbles (HFSB) as tracers. The measurement volume is several orders of magnitude larger than that reported in tomographic experiments dealing with pressure from particle...

A quantitative flow visualization technique for on-site sport aerodynamics optimization

Aerodynamics plays a crucial role in cycling as in many other speed sports. Aerodynamic investigation is required primarily for two reasons:<br/><br/>1. Optimization of the athletes' posture and equipment geometry (e.g. bicycle frame, wheels, helmet) to minimize the aerodynamic drag, thus achieving higher velocity;<br/>2. Enhancement of the...

A seeding system for large-scale Tomographic PIV in aerodynamics